1. Field of the Invention
The present invention relates to an electromagnetic fuel injector for an internal combustion engine.
2. Description of Related Art
In an electromagnetic fuel injection valve (sometimes called an injection valve), opening and closing operation is performed by controlling an electromagnetic coil in energizing with current and interrupting, and while the valve is opened, a fuel is injected to a intake air passage, a intake port or a combustion chamber.
As such an injector, a system is put to practical use, where in order to improve rising characteristics while a valve is opened, high voltage is produced by providing a drive circuit with a booster circuit, and while the high voltage is impressed to a coil of the injector, a current control circuit is used and a large current is forced to flow at a short time (for example, JP-A 6-241137). In the system, a battery voltage (for example, 12V) is raised (for example, 70V) during the valve opening. Particularly, as, an applied injector, there is an injector in intracylinder injection system where a fuel pressure is high and a load in a return spring is large (an injector where a fuel is injected directly into a combustion chamber of a gasoline engine).
In an injector using a booster circuit, when a valve is opened as already described, while a large voltage is impressed to an electromagnetic coil, a large current flows in the coil.
After the valve is opened, since a fuel pressure within the injector decreases and a return spring is not in the state of set load, force for holding the opened valve does not require magnetomotive force in comparison with the case of opening the valve. Accordingly while the opened valve is held, the voltage to the coil is changed from the booster circuit into the battery voltage, and in the coil a relatively small current enough to hold the opened valve is flowed by using a current control circuit.
Further in recent years, technology is proposed where a booster circuit is not used and rising characteristics during the valve opening are improved by a system impressing a battery (for example, JP-A 11-148439). In this system, two types of electromagnetic coils different in wire diameter and the number of turns of the coils are prepared. Among these, the first coil is mainly used during the rising operation while the valve is opened (the operation that the valve moves from the closed position to the fully opened position), and as characteristics, time variation rate of the magnetomotive force is made large. Therefore in the first coil, the wire diameter is made relatively large (the coil resistance is made small), and the number of turns is made small and a large current flows in the coil with good response. Also since the current is made large, the magnetomotive force is raised.
The second coil is mainly used to hold the state after the valve is opened. Accordingly the response property as in the case of the first coil is not required, and the large magnetomotive force as in the case of opening the valve is not required. The time variation rate of the magnetomotive force may be small. Accordingly in the second coil, the wire diameter is made relatively small (the coil resistance is made large) and the number of turns is made large, and the magnetomotive force capable of holding the opened valve even at a small current is obtained.
In the battery voltage drive system, a booster circuit and a current control circuit as above described are not required. Accordingly the system is advantageous in that the cost reduction can be intended.
As above described, in the electromagnetic fuel injector valve, in order to raise the output characteristics and the response property, proposals are made and that the coil impressed voltage is raised and the coil current is made large, or two types of the electromagnetic coils different in the characteristics are used. With accompanying this, the countermeasure for heat generated in the coil is further required. Particularly an intense heat of the coil under the violent state of the high temperature circumstances such as the inside of the engine room deteriorates the state of the insulation film and the bobbin of the coil and results in the reduction of the life. Accordingly the countermeasure for the intense heat generated in the coil is necessary.
Besides the countermeasure for the intense heat, when the first coil and the second coil different in the characteristics are prepared as above described, the number of the coil terminals increases. Therefore the problems remain in that how these terminals and other parts are made intensive and rationalized and the injector is realized at compact structure and low cost.
An object of the present invention is to provide an injector in which these problems are solved and the heat radiation property of the coil of the injector accompanied by the performance improvement is raised, and which can entirely withstand the environment of the intense heat and assures its long life and moreover can intend to achieve the compact structure and the cost reduction.
In order to attain the foregoing object, the present invention is basically constituted as follows.
One is an injector with an electromagnetic coil for driving a valve, considering the heat radiation performance of the coil, where a bobbin for winding the coil thereon is constituted by a synthetic resin containing a filler having good heat conductivity.
Another is an injector where an electromagnetic coil for driving a valve is provided with two types of coils different in the characteristics, and these coils are wound separately in the axial direction of one bobbin, and among these coils, the winding region of one coil (the first coil) is near a movable core with a valve element being the object of the magnetic suction and the winding region of the other coil (the second coil) is away from the movable coil, and where the bobbin has a step difference of the outer diameter so that the bobbin outer diameter in the region with the second coil to be wound thereon is smaller than the bobbin outer diameter in the region with the first coil to be wound thereon, and on the other hand, the bobbin inner diameter in the region with the first coil to be wound thereon is partially enlarged and the step difference of the inner diameter is formed so that the annular space to interpose the seal ring is secured.
Another is an injector having a first coil and a second coil different in characteristics as above described in order to intend simplification and rationalization of parts, where a connector part comprising three terminals is provided, and the above-mentioned first and second coils are connected to the power source and two switching elements for energizing control through the three terminals.
In order that electromagnetic coil relevant parts are made intensive and compact, another injector is constituted as follows.
That is, in an electromagnetic fuel injector where a first coil and a second coil as above described are arranged in the axial direction of one bobbin, and a connector part to connect terminals of these coils to an external power source and a switching elements is provided to project laterally at the upper side of the bobbin as above described,
characterized in that plural terminals of said first and second coils are arranged on the upper end surface of said bobbin, and at least one of these terminals has the base part positioned at the opposite side of the connector part with respect to the axial line of the main body of the injector, and this terminal has a curved part formed at the midway led from the base part to the connector part so as to avoid the axial line.